When users visit your site, the browser will display a small window(opt-in) prompting them to register. They must do so in order to receive web push notifications. 

Once they’ve subscribed, notifications you send will be displayed on the subscriber’s screen, even when they’re not on your website.You can start by sending them a welcome notification or any upcoming big announcement. This is an example of simple notification. 

You can send a large image notification which looks like this:-

You can also add multi-action with large image notification large image notification.

The Large image makes your desktop notification stand out and increase Click Rates. This works on Chrome (version 56+).